1. Field of the Invention
The present invention relates to a method and apparatus for making photographic light-sensitive material wherein a photographic emulsion is coated on a support web, such as photographic film, Baryta paper and the like, and thereafter irradiated with microwave energy before cooling and setting to thereby concentrate the coating and decrease the overall drying time.
1. Description of the Prior Art
In the past, photographic film has been made by coating a light-sensitive emulsion on a web, cooling and setting the coating, and thereafter using ordinary air to dry the coating under controlled humidity conditions, and it is a natural tendency to try to increase the coating speed in order to enhance production capacity. Since the coating and drying steps in manufacturing a film are conducted in a continuous manner, if the web transport speed is increased to increase the coating speed, the drying time becomes shortened if the drying zone is constant in length. Generally speaking, if the drying capacity is constant, the degree of drying progress is proportional to the drying time, resulting in difficulty in achieving sufficient drying. For this reason, it is necessary to lengthen the drying zone corresponding to the rate of increase in the coating speed to accomplish sufficient drying. This is difficult to realize, however, in terms of both space and the cost of the added installation. To achieve sufficient drying, additional means must thus be provided to relieve the drying load in order to meet the needs of hgh speed coating.
To relieve such drying load, two methods have been proposed to provide a concentrated photographic emulsion prior to its application to the web. One method is to concentrate the photographic emulsion during its formation process, and thereafter various chemicals are added and mixed with the emulsion. In the other method, the emulsion is firstly mixed with various chemicals, and thereafter the mixture is concentrated by a condenser, such as an evaporator, immediately before coating. In the former method, it is difficult to provide a uniform mixture when various chemicals are added after the emulsion has been produced, whereby the quality of the product might be increased. In the latter method, some problems occur, such as a pressure loss when the condensed emulsion is fed to a coating device, difficulty in removing generated bubbles, and difficulty in washing the coating device. Also, in both methods the condensed emulsion results in a decreased quantity of coating per unit area of the web, which results in the necessity of applying the coating in a thin layer, and it is difficult to provide a uniform coating due to the higher viscosity of the coating liquids.